Effects of radionuclide contamination on leaf litter decomposition in the Chernobyl exclusion zone

The effects of radioactive contamination on ecosystem processes such as litter decomposition remain largely un- known. Because radionuclides accumulated in soil and plant biomass can be harmful for organisms, the function- ing of ecosystems may be altered by radioactive contamination. Here, we tested the hypothesis that decomposition is impaired by increasing levels of radioactivity in the environment by exposing uncontaminated leaf litter from silver birch and black alder at (i) eleven distant forest sites differing in ambient radiation levels (0.22–15 μGy h−1) and (ii) along a short distance gradient of radioactive contamination (1.2–29 μGy h−1) within a single forest in the Chernobyl exclusion zone. In addition to measuring ambient external dose rates, we estimat- ed the average total dose rates (ATDRs) absorbed by decomposers for an accurate estimate of dose-induced eco- logical consequences of radioactive pollution. Taking into account potential confounding factors (soil pH, moisture, texture, and organic carbon content), the results from the eleven distant forest sites, and from the single forest, showed increased litter mass loss with increasing ATDRs from 0.3 to 150 μGy h−1. This unexpected result may be due to (i) overcompensation of decomposer organisms exposed to radionuclides leading to a higher decomposer abundance (hormetic effect), and/or (ii) from preferred feeding by decomposers on the un- contaminated leaf litter used for our experiment compared to locally produced, contaminated leaf litter. Our data indicate that radio-contamination of forest ecosystems over more than two decades does not necessarily have detrimental effects on organic matter decay. However, further studies are needed to unravel the underlying mechanisms of the results reported here, in order to draw firmer conclusions on how radio-contamination affects decomposition and associated ecosystem processes

Current evidence for a role of epigenetic mechanisms in response to ionizing radiation in an ecotoxicological context

The issue of potential long-term or hereditary effects for both humans and wildlife exposed to low doses (or dose rates) of ionising radiation is a major concern. Chronic exposure to ionising radiation, defined as an exposure over a large fraction of the organism's lifespan or even over several generations, can possibly have consequences in the progeny. Recent work has begun to show that epigenetics plays an important role in adaptation of organisms challenged to environmental stimulae. Changes to so-called epigenetic marks such as histone modifications, DNA methylation and non-coding RNAs result in altered transcriptomes and proteomes, without directly changing the DNA sequence. Moreover, some of these environmentally-induced epigenetic changes tend to persist over generations, and thus, epigenetic modifications are regarded as the conduits for environmental influence on the genome. Here, we review the current knowledge of possible involvement of epigenetics in the cascade of responses resulting from environmental exposure to ionising radiation. In addition, from a comparison of lab and field obtained data, we investigate evidence on radiation-induced changes in the epigenome and in particular the total or locus specific levels of DNA methylation. The challenges for future research and possible use of changes as an early warning (biomarker) of radiosensitivity and individual exposure is discussed. Such a biomarker could be used to detect and better understand the mechanisms of toxic action and inter/intra-species susceptibility to radiation within an environmental risk assessment and management context

COMET deliverable (D-No. 1.5). COMET project final report: advancement in science, integration and sustainability of European radioecology

The EC FP7 COMET (Coordination and iMplementation of a pan-European instrument for radioecology) was funded to strengthen the pan-European research initiative on the impact of radiation on man and the environment by facilitating the integration of radioecology research and development

Exposition chronique et génotoxicité : quelle conséquence sur la santé ?: Étude des effets d’une exposition chronique à de faibles doses de stresseurs génotoxiques à l’aide du modèle biologique Caenorhabditis elegans

Pour comprendre le lien de causalité entre des expositions chroniques à de faibles doses d’agents cancérogènes et l’apparition du cancer, il est donc indispensable de caractériser les mécanismes physiologiques, cellulaires et moléculaires sous-jacents au processus de cancérogénèse. L’originalité de ce programme de recherche repose sur l’utilisation du nématode Caenorhabditis elegans comme modèle biologique. En effet, un grand nombre de voies de régulation sont communes entre C. elegans et l’homme

Importance of water chemistry for the toxicity of uranium on an aquatic organism

Uranium (U) is a radioactive element found at trace concentrations throughout the natural environment. Its level can increase in association with human activities associated with nuclear fuel cycle. The aim of our studies was first to investigate the influence of water chemistry on acute toxicity of uranium on Daphnia magna. Acute uranium toxicity for Daphnia magna was determined in two different exposure media, differing in pH and alkalinity. LC50 varied strongly between media, from 390+-40 g.L-1 U at pH 7 to 7.8+-3.2 mg.L-1 U at pH 8. According to the free ion activity model uranium toxicity varies as a function of free uranyl activity. This assumption was examined by calculating uranium speciation in our water conditions and in those reported in the literature. Predicted changes in free uranyl concentration could not solely explain observed differences in toxicity, which might be due to a competition or a non-competitive inhibition of H+ for uranium transport and/or the involvement of other bioavailable chemical species of uranium. Uranium toxicity was also compared to the toxicity of other alpha-emitting radionuclides and stable trace metals. Our results confirmed the general assumption that uranium chemical toxicity predominates over its radiotoxicity

Effects of waterborne uranium on survival, growth, reproduction and physiological processes of the freshwater cladoceran Daphnia magna

International audienceAcute uranium toxicity (48 h immobilisation test) for Daphnia magna was determined in two different exposure media, differing in pH and alkalinity. LC50 varied strongly between media, from 390 +/- 40 mu g L-1 U at pH 7 to 7.8 +/- 3.2 mg L-1 U at pH 8. According to the free ion activity model uranium toxicity varies as a function of free uranyl concentration. This assumption was examined by calculating uranium speciation in our water conditions and in those reported in the literature. Predicted changes in free uranyl concentration could not solely explain observed differences in toxicity, which might be due to a competition or a non-competitive inhibition of H+ for uranium transport and/or the involvement of other bioavailable chemical species of uranium.Chronic effects of uranium at pH 7 on mortality, ingestion and respiration, fecundity and dry mass of females, eggs and neonates were investigated during 21-day exposure experiments. A mortality of 10% was observed at 100 mu g L-1 U and EC50 for reproduction was 14 +/- 7 mu g L-1 U. Scope for growth was affected through a reduction in feeding activity and an increase in oxygen consumption at 25 mu g L-1 U after 7 days of exposure. This had strong consequences for somatic growth and reproduction, which decreased, respectively, by 50% and 65% at 50 mu g L-1 U after 7 days and at 25 mu g L-1 U after 21 days. Uranium bioaccumulation was quantified and associated internal alpha dose rates from 2.1 to 13 mu Gy h(-1) were estimated. Compared to the toxicity of other alpha-emitting radionuclides and stable trace metals, our results confirmed the general assumption that uranium chemical toxicity predominates over its radiotoxicity

Heavy metal accumulation by recombinant mammalian metallothionein within Escherichia coli protects against elevated metal exposure.

International audienceMetallothioneins (MTs) are ubiquitous metal-binding, cysteine-rich, small proteins known to provide protection against toxic heavy metals such as cadmium. In an attempt to increase the ability of bacterial cells to accumulate heavy metals, sheep MTII was produced in fusion with the maltose binding protein (MBP) and localized to the cytoplasmic or periplasmic compartments of Escherichia coli. For all metals tested, higher levels of bioaccumulation were measured with strains over-expressing MBP-MT in comparison with control strains. A marked bioaccumulation of Cd, As, Hg and Zn was observed in the strain over-expressing MBP-MT in the cytoplasm, whereas Cu was accumulated to higher levels when MBP-MT was over-expressed in the periplasm. Metal export systems may also play a role in this bioaccumulation. To illustrate this, we over-expressed MBP-MT in the cytoplasm of two mutant strains of E. coli affected in metal export. The first, deficient in the transporter ZntA described to export numerous divalent metal ions, showed increasing quantities of Zn, Cd, Hg and Pb being bioaccumulated. The second, strain LF20012, deficient in As export, showed that As was bioaccumulated in the form of arsenite. Furthermore, high quantities of accumulated metals, chelated by MBP-MT in the cytoplasm, conferred greater metal resistance levels to the cells in the presence of added toxic metals, such as Cd or Hg, while other metals showed toxic effects when the export systems were deficient. The strain over-expressing MBP-MT in the cytoplasm, in combination, with disruption of metal export systems, could be used to develop strategies for bioremediation

Nested interactions in the combined toxicity of uranium and cadmium to the nematode Caenorhabditis elegans

Uranium is a natural, ubiquitous radioactive element for which elevated concentrations can be found in the vicinity of some nuclear fuel cycle facilities or intensive farming areas, and most often in mixtures with other contaminants such as cadmium, due to co-occurrence in geological ores (e.g. U- or P-ore). The study of their combined effects on ecosystems is of interest to better characterize such multi-metallic polluted sites. In the present study, the toxicity of binary mixture of U and Cd on physiological parameters of the soil nematode Caenorhabditis elegans was assessed over time. Descriptive modeling using concentration and response addition reference models was applied to compare observed and expected combined effects and identify possible synergistic or antagonistic interactions. A strong antagonism between U and Cd was identified for length increase and brood size endpoints. The study revealed that the combined effects might be explained by two nested antagonistic interactions. We demonstrate that the first interaction occurred in the exposure medium. We also identified a significant second antagonistic interaction which occurred either during the toxicokinetic or toxicodynamic steps. These findings underline the complexity of interactions that may take place between chemicals and thus, highlight the importance of studying mixtures at various levels to fully understand underlying mechanisms